The invention concerns an element for the determination of an analyte in a liquid by means of a specific binding reaction of two bioaffine binding partners containing in or on material which enables liquid transport between zones, a sample application zone and a detection zone located downstream thereof and a zone containing immobilized analyte or analyte analogue between the sample application zone and detection zone, and impregnated conjugate that can be detached by liquid and is located in the sample application zone or upstream or downstream thereof composed of a bioaffine binding partner capable of a specific binding reaction with the analyte to be determined and a detectable label.
Such elements are known for example from DE-A3842702 or DE-A4439429. The described analytical elements contain the necessary reagents to carry out immunoenzymometric or immunoenzymometric-like methods of determination. In particular these are analyte or analyte analogue immobilized in a zone, between the sample application zone and detection zone and a conjugate composed of a bioaffine binding partner capable of a specific binding reaction with the analyte to be determined and a detectable label.
In the case of DE-A 3842702 an enzyme label is described as the detectable label. In order to make this label visible it is necessary to contact it with a chromogenic enzyme substrate such that a colour is formed as a result of the enzymatic activity. The requirement that the label has to be made visible is a complication, costly due to the measures that have to be taken and furthermore may result in technical difficulties for example when the corresponding enzyme substrate has stability problems in the analytical element.
Therefore recently direct labels have been preferred as described in DE-A 4439429. These direct labels are for example metal or latex particles which have an intrinsic colour and can be visualized with the naked eye. Nowadays a gold label is particularly preferred. For this an appropriately labelled bioaffine binding partner depending on the analyte is prepared for which optimal conditions then have to be created on the analytical element for reaction and storage. This individual adaptation to the analyte to be determined is very laborious. Depending on the analyte to be determined, the required polyclonal or monoclonal antibodies can behave very differently when conjugated to gold particles. This can lead to different stabilities of gold conjugates. The differences in the behaviour of the various polyclonal antibodies or various monoclonal antibodies when coated on gold particles can result in quite different spatial arrangements of the antibodies on the gold particles which leads to steric problems when such conjugates are reacted with the analyte and can thus result in a poor sensitivity.
The object of the present invention was therefore to avoid these disadvantages and to provide an analytical element containing stable reagents that can be produced simply and reproducibly and which enables a sensitive determination reaction.
This object is achieved by the subject matter of the invention as described in the claims.
The invention concerns an element for the determination of an analyte in a liquid by means of a specific binding reaction of two bioaffine binding partners    containing in or on material which enables liquid transport between zones, a sample application zone and a detection zone located downstream thereof    as well as a zone containing immobilized analyte or analyte analogue between the sample application zone and detection zone    and an impregnated conjugate 1 upstream of the zone containing immobilized analyte or analyte analogue that can be detached by liquid and is composed of a bioaffine binding partner 1 capable of a specific binding reaction with the analyte to be determined and a detectable label 1,    characterized in that    the detectable label 1 is a low molecular organic molecule and a universal conjugate 2 is present upstream of the zone containing immobilized analyte or analyte analogue which can also be detached by liquid and is composed of a bioaffine binding partner 2 capable of a specific binding reaction with the detectable label 1 and a visually detectable label 2.
The invention additionally concerns the use of an element according to the invention to determine an analyte and a corresponding method of determination. This method for the determination of an analyte by means of an element according to the invention is characterized in that    a sample application zone is contacted with analyte,    the analyte is moved by liquid towards the detection zone,    analyte present in this liquid reacts with conjugates 1 and 2 to form a detection complex,    the detection complex is transported by liquid into the detection zone    and is determined there.
Finally the invention concerns a kit for the determination of an analyte containing an analytical element according to the invention and an elution agent.